Suffocating Dogs?

No doubt someone has answered this before but I really want to know for sure!

I was drining along a country lane yesterday and the car in front had one of its rear windows down and their black labrador had its head out the window. The car was doing at least 50 mph so I can’t believe the dogs was able to smell that much. So, why do dogs seem to love having their heads out the windows of moving cars? Do the insides of cars smell that bad?

Thanks for your help.